1. Field of the Invention
The invention relates to a biological control agent for control of fungal diseases in plants.
2. Description of the Prior Art
Trichoderma virens (formerly known as Gliocladium virens) has been recognized as a mycoparasite and antibiotic-producing antagonist of plant pathogens, and has been used as an effective biocontrol agent of several soilborne root or seedling diseases Aluko and Hering, 1970, Trans. Br. Mycol. Soc., 55:173-179; Beagle-Ristaino and Papavizas, 1985, Phytopathology, 75:560-564; Howell, 1982, Phytopathology, 72:496-498; Howell and Stipanovic, 1983, Can. J. Microbiol., 29:321-324; Weindling and Fawcett, 1936, Hilgardia, 10:1-16; and Wright, 1956, Plant Soil, 8:132-140!. T. virens produces gliotoxin and gliovirin, which are particularly effective antifungal antibiotics, as well as the antibacterial compound heptelidic acid and the antifungal compound viridin.
In addition to its use as an antifungal biocontrol agent, T. virens has also been employed as a mycoherbicide Jones et al., 1988, Weed Science, 36:683-687; and Howell and Stipanovic, 1984, Phytopathology, 74:1346-1349!. Herbicidal activity has been attributed to the production of viridiol, a steroidal phytotoxin which is very toxic to the growing tip of the emerging radicle of a germinating seedling and results in necrosis of the meristematic tissue and severe stunting of the root.
Unfortunately, viridiol has not only been shown to be phytotoxic to weeds such as pigweed, but also to valuable crop plants such as cotton seedlings Howell et al., Phytopathology, 74:1346-1349 (1984)!. Thus, the production of the phytotoxic compound viridiol may severely restrict the use of T. virens as a biocontrol agent for the control of plant diseases, limiting the amount of T. virens that can be applied to crops and/or seeds.
This problem can be partially alleviated by the addition of sterol inhibiting fungicides to the developing fungus cultures as described by Howell (U.S. Pat. No. 5,268,173, the contents of which are incorporated by reference herein). However, excessive levels of these fungicides tend to inhibit the growth of the T. virens, and do not prevent subsequent production of phytotoxin by the fungus around the seed after planting.